This invention relates to closure devices and fastening means for pipes, tanks and various other tubular shaped fluid enclosures, which are generally subjected to high internal pressure.
A common device for fastening such tubular members to one another empolys a plurality of bolts which pass through radially extending flat flanges provided on the ends of the tubular members. One problem inherent in such a device is that it is often difficult to accurately align the end flanges with one another in order that the bolts may be placed through the holes. This problem is accentuated when relatively heavy tubular members, such as pipeline segments, are required to be secured to one another. A further disadvantage of the use of bolts to secure the flat end flanges is that due to the diameter of the bolt head and the need for engaging the bolt heads with wrenches that fit over them the flanges must extend a considerable distance from the pipe or vessel wall. Consequently, the axial forces produced by the bolts are applied at a substantial distance from the pipe or vessel wall, thereby resulting in bending moments and adverse stresses about the ends of the pipe or vessel segments.
Most recently, tubular members have been secured to one another with radially protruding, tapered end flanges extending around the circumference of the open ends of the tubular members. Like the flat flanges, these flanges also have flat mating faces. However, the back sides of the flanges are tapered, i.e. they define a conical surface which diverges in a radially outward direction towards the open end of the tubular member. Thus when the mating faces of two pipes or vessels are abutted against one another, the backs of the mated flanges converge radially outwardly from the pipes or vessels. A yoke or split ring device having a groove shaped so as to generally match the mated flanges is then used to clamp the pipe or vessel segments together. The split ring comprises two semi-circular segments. The two segments of the ring are placed over the mated flanges and the ends of the two ring segments are secured together with bolts which are oriented tangentially to the completed ring. As the bolts are tightened the grooves of the ring apply axial clamping forces to the tapered back sides of the mated flanges. A split ring fastening device of this type is described in U.S. Pat. No. 3,077,360.
Although such an arrangement is a substantial improvement over the earlier discussed bolted flange connection, it has several disadvantages. The flanges are difficult to align, especially when the pipe or vessel segments are heavy, e.g. when the segments are adapted for high pressure application. Because the flanges are machined in various sizes and shapes, a separate split ring is required to accommodate each specific flange size. Additionally, the tapered back sides of the flanges have various irregularities around their circumference either because of normal machining tolerances or because of galling and wear caused by frequent use. Accordingly, the axial thickness of the mated flanges may vary considerably around the circumference. Thus when the split ring segments are attached and bolted together, the axial clamping forces are not always equally distributed around the circumference of the mated flanges and adverse bending moments and stresses result. A further disadvantage of the split ring connection occurs because the ring normally contacts the flanges around the entire circumference, and thus the ring is often extremely difficult to remove because of rust or corrosion which may have developed after exposure to the atmosphere for an extended time period.